This disclosure relates generally to filtering wastewater in a septic system, and, more particularly, to filtering wastewater in a secondary septic containment space and thereafter discharging the filtered effluent from the secondary septic containment space.
Treating wastewater such as sewage wastewater from residential or commercial buildings often includes collecting the raw untreated sewage in a wastewater containment space such as a septic tank. The untreated sewage having a significant concentration of waste solids flows into the septic tank whereafter solids separate from the liquid portion of the sewage. Solids having a lower density than the liquid move to the top of the liquid to form a scum layer, and solids having a higher density than the liquid sink to the bottom of the tank to form a sludge layer. Between the lower horizontal sludge layer and the upper horizontal scum layer a relatively clear liquid layer forms. Liquid from the relatively clear liquid layer is then typically filtered and discharged from the septic tank into a leach field or a secondary septic tank, or perhaps recirculated back into the primary septic tank depending upon such factors as the amount of waste solids remaining in the filtered effluent or other quality aspects of the filtered effluent, liquid loadings and other characteristics of the soil system (or leach field), capacities of the septic system to receive and treat wastewater during periods of peak flow, and various other factors, including local environmental regulations. Various systems may be designed to suit particular applications, but most systems include at least one septic tank, a leach field, and gravity-fed or active means of flowing effluent from the septic tank into the leach field.
In a gravity-fed system, effluent flows from a septic tank whenever wastewater is received into the tank causing the wastewater level in the tank to rise above the level of an effluent outlet. More sophisticated systems attempt to more evenly control liquid loadings into the soil system by intermittently discharging (or dosing) effluent from the septic tank with the use of an effluent pump. Such dosing systems commonly use float switches and timers to control the effluent pump and the amount and frequency of effluent discharged from the septic tank. The float switches are typically protected from becoming fouled within the septic tank by a protective open-topped housing that extends vertically from a lower level in the septic tank to above a maximum wastewater level of the tank, as disclosed in U.S. Pat. Nos. 5,492,635 and 5,531,894.
Wastewater treatment systems having more than a single septic tank or wastewater containment space may be used to further improve effluent quality before permanently discharging effluent from the septic system. For example, untreated wastewater may flow into a primary septic tank within which the waste solids distribute into a lower sludge layer, an upper scum later, and a relatively clear layer of liquid therebetween. Liquid from the relatively clear layer in the primary tank is then flowed into a secondary tank or secondary wastewater containment space. Even if the relatively clear liquid from the first septic tank is filtered before being discharged from the primary tank, a concentration of waste solids remains within the effluent received from the primary tank. Therefore, waste solids in the effluent received into the secondary tank from the primary tank will similarly distribute within the secondary tank into a horizontal lower sludge layer, a horizontal upper scum layer, and a relatively clear liquid layer therebetween. Liquid from the relatively clear liquid layer within the secondary tank may then be filtered and intermittently discharged from the secondary tank into a leach field or fed into a further wastewater treatment subsystem.
Exemplary systems which utilize a secondary wastewater containment space are disclosed in U.S. Pat. Nos. 5,531,894; 6,372,137; and 6,540,920. All of those systems involve flowing wastewater from the relatively clear liquid layer within the secondary containment space through a filter that is surrounded by an open-topped housing that extends vertically from a lower level in the secondary containment space to above a maximum wastewater level of the secondary containment space. The housing in each of those systems surrounds a submergible pump, one or more filtering elements, and float switches so as to prevent exposure of those components to the horizontal lower sludge layer and horizontal upper scum layer within the secondary containment space.
Although they may be effective for wastewater treatment generally, filtration and effluent discharge systems designed for use in primary septic tanks or systems having a single wastewater containment space are not optimized for secondary containment space applications. Filtration and effluent discharge systems designed to function within a secondary containment space, or in a separate tank following a primary septic tank, are desirable, especially if such systems can be made smaller and lighter. Smaller and lighter filtration and effluent discharge systems are needed that are easier to install and remove, clean, and replace during maintenance. Smaller and lighter systems are needed that require less material and are, therefore, less expensive to manufacture and sell.